Combined heat and power (CHP) is generally known, and is usually also referred to as cogeneration of heat and power (CHP). Combined heat and power is to be understood to mean the simultaneous production of mechanical energy, which is normally converted into electric current, or electrical energy, and of usable heat for heating purposes or, possibly, for production purposes.
Usually, residential units and industrial enterprises as far as possible have electricity and heat supplied by a central infrastructure in the form of an electric power grid and a heat grid. Also becoming more prevalent are the purchase of electricity from the central infrastructure, and a decentralized supply of heat, for example effected by means of a gas-fired boiler and/or oil-fired boiler. This ensures a reliable supply of electricity and heat, including the covering of peak loads.
In times of increasing costs of central energy supply, the decentralized generation, or provision, of heat and electrical energy becomes ever more important. For example, photovoltaic systems and/or wind power plants are used to realize a decentralized electricity supply. Owing to a relatively stable gas price and a high fuel efficiency, however, combined heat and power is also becoming very important in the decentralized sphere. Combined heat and power plants usually have an engine for providing electrical energy. The engine in this case comprises at least one engine element by means of which mechanical energy is provided by combustion of fuel. In other words, the engine can convert energy stored in fuel into mechanical energy, and provide this mechanical energy. In addition, the engine comprises at least one generator that is coupled to the engine element, and to which the mechanical energy provided by the engine element is supplied. By means of the generator, the provided mechanical energy is converted into electrical energy, such that, overall, the engine can provide electrical energy.
Alternatively, in the case of a fuel cell, the fuel energy can also be converted directly into electrical energy and thus, overall, electrical energy can be provided.
For example, spark-ignition engines, diesel engines and/or Stirling engines, and fuel-cell systems, can be used as engines or engine elements. These combined heat and power plants typically have a constant ratio of electricity generation to heat generation. Their flexibility with respect to varying electricity and heat generation is greatly limited. The combined heat and power plants can be operated in part-load operating mode, but then at the same time there is decreased generation of electricity and heat. Consequently, a demand for electricity and heat that varies over time cannot be serviced. For this reason, such combined heat and power plants are now used only for additional supply of electricity and heat, in order to cover a base load. In order to achieve sufficient flexibility and to cover peaks in demand, there is still a need for an electrical grid connection for the supply of electricity and, for example, for a fuel-fired peak-load boiler for the supply of heat.